To find all surrounding mobile radio cells, a mobile radio communication terminal device such as a user equipment (UE) usually needs to activate frequency scan and cell scan (also together called Public Land Mobile Network (PLMN) search) procedure in some cases. A typical example is when a user just enters a new country and thus his/her mobile radio communication terminal device does not have any prior knowledge about its surrounding mobile radio communication networks. In these cases, the scan speed may be important, since it directly impacts user experience (a user will probably not be happy if he/she has to wait for a couple of minutes before his/her mobile radio communication terminal device attaches a mobile radio communication network, when for example, he/she walks out of an airplane).
A conventional Public Land Mobile Network (PLMN) search usually consists of two consecutive processes, namely a frequency scan and a mobile radio CELL scan. The frequency scan is performed first for all candidate Enhanced Universal Mobile Telecommunications System (UMTS) Radio Access (E-UTRA) Absolute Radio Frequency Channel Numbers (EARFCNs) to identify frequencies, which most likely contain a mobile radio cell. After the frequency scan, the mobile radio cell scan is performed for each EARFCN in a so-called short list to check whether there exist mobile radio cells or not.
Several factors together usually contribute to the speed of the frequency/cell scan procedure. They are mainly frequency scan time, quality of frequency scan output (i.e. mobile radio cell scan input), and cell scan time per EARFCN.
In the conventional PLMN search method, the time spent on the frequency scan can be quite long when the number of candidate EARFCNs is large. In a Long Term Evolution (LTE) system, 692 total EARFCNs are specified.
In a conventional frequency scan, Received Signal Strength Indication (RSSI)-based frequency scan is used. With RSSI-based frequency scan, time spent during frequency scan is normally short. However, due to its vulnerability to interference from other radio access technology (RAT), the quality of frequency scan output can be quite poor in an LTE mobile radio communication network. Thus, time spent on an entire PLMN search could be quite long and intolerable.